I'll assume that you have either a Mac or PC... and I'll further assume that you have a separate, older Mac that has the old connection ports that pre-date USB.
I don't know what platform you're running Sheepshaver on, but I doubt that SheepShaver (currently) has the capability to utilize any "Ir" hardware on the host computer (PC or Mac). If somebody else here can prove me wrong, don't hesitate to do so!
You should be able to find someone selling the Newton Connection Kit (along with a functional Newton 100!) on eBay... I found it... looks like the seller wants $10.00 (U.S.) for it... best part is that he's throwing in all the Mac software you need to use it...http://www.ebay.com/itm/Apple-Newton-MessagePad-with-Instructions-and-Accessories-/251077290014?pt=US_Vintage_Computers_Mainframes&hash=item3a755f681e
On the other hand, if you are up to the challenge, you can do what this other guy did back in 1995; he made his own Newton connection cable (for PC). http://www.nsbasic.com/newton/info/technotes/cable.html
As for the appropriate software tools/drivers you'd need for a "Newton-to-PC" scenario, i'm afraid I can't help you on that one...
For further reading (yes, I realize they're not related to Sheepshaver), you might also consider this page:http://www.deleet.de/ray/newton/802.11b-FAQ.html
...and this page:http://www.drvlabo.jp/old/eng/newte.htm